fender deluxe reverb 65 repair

[tepsamps]

Please check for bias voltage at pin 5 on both 6V6 sockets. If you have have about -35V to -40V then please interpret "crappy" and "bad" more clearly. And report on other things like plate voltages and whether all the controls are working.

Like crunching but nasty way. And with the reverb it was making like a feedback fast...

[tepsamps]

Octal tube sockets are designed with the individual female contacts floating within the body of the socket assembly. Therefore, it is normal for the tube to feel loose. This design feature is purposely done to allow each pin socket to align with the male tube pins while preventing excessive side stress to the tube base.

That's not a great solution because it will raise the high voltage and will also change the character of the amp. It appears that you got a bad new rectifier. Unfortunately, this is fault does happen with modern tubes.

The rectifier tube was easy to put and to remove...
What does it change in the amp with diodes? Tonally i mean...

I always built amps with diodes rectifiers...

[tepsamps]

Before the problem the amp has some farting noises or like some fridge noises added to the common hum noise....A noise that appears and desappears after 10 or 20 sec... My first amps were like this i think...
The wiring is not that good, ground points anywhere, long leads, audio and electric wires twisted together...
No HV fuse...

I nearly forgot... I found a broken resistor, a big carbon 470 R 1 watt on the G2 grid position on one tube.

And i had noticed that this 6V6 were more shiny than the other...

I hope the OT is still good...

[Helmholtz]

The '65 Deluxe Reverb (model AB763) is considered one of the best sounding Fender amps ever made by many players.
I do not recommend to modify the amp..

Rather start troubleshooting:
- Replace power tubes and
- verify schematic voltages.

Can you read schematics?
Do you have a scope?

[g1]

The tone issues are not necessarily related to the rectifier issue. It may just be coincidence and you might have multiple faults with the amplifier.

[Tom Phillips]

The rectifier tube was easy to put and to remove...What does it change in the amp with diodes? Tonally i mean...I always built amps with diodes rectifiers...

The bottom line is that changing from a tube to a solid state rectifier is not a like-for-like swap.

Tube rectifiers have inherent series resistance which is much higher than the series resistance of solid state rectifier diodes. Therefore, changing to a solid state rectifier, without making other changes to the amp will result in the following:
1) The DC power supply voltage will increase. The plate voltage of the stock Deluxe Reverb is already high and I personally, don't like to increase it further.
2) Any plate voltage change will require re-setting the bias.
3) Without the sag caused by the resistance of the tube rectifier, the response and feel of the Deluxe Reverb will change. It will be punchier and tighter and produce a little more output power. Only the owner can decide if they like the new feel better. However, the new performance will be a departure from the classic DR.
There are things that can be done to compensate for these effects but that just adds more modification chores.

Keep in mind that Fender could have changed the DR design to use a SS rectifier as the amp evolved over the decades. That would have saved some manufacturing cost without changing the "on paper" specifications. It's notable that they did not choose to do that.

[tepsamps]

I won't modify the rectifier... I swear

I have a layout i found on the web, and there are some changes in the power supply in my DR.

First, when i changed the paper cap in the cap room, there were one 10 k and one 2.2 k instead of two 10 k. I put two 10 k 2 watts metal film instead.

I start the amp and it was working good.

So i've changed the rectifier socket, and i tried to stick to the schematic. I changed also the G2 resistors with new ones, but metal film.

I have a lot of checking to do now...

[g1]

I try to avoid changing values to match schematics unless I can guarantee someone put in the wrong part in a previous repair. There are too many versions of schematics and what happens in production can vary. Any changes you introduce during the repair process are suspect if you still have problems.

[tepsamps]

The amp seems to work fine, but something is weird...

On the chassis, there are marks of heat around the rectifier tube socket and only one power tube socket. So one tube seems to heat less.
I put a 1 ohm resistor on the cahode to ground on both tubes. The bias voltage was -37 V, the hot tube is at 36 mA and the cold one is at only 17 mA, so it's not good for paired tubes.
These are the new tubes i bought recently and it matches the heat marks on the chassis. Tomorrow i switch the tubes to check of course...

[Tom Phillips]

... The bias voltage was -37 V, the hot tube is at 36 mA and the cold one is at only 17 mA, so it's not good for paired tubes.
These are the new tubes i bought recently and it matches the heat marks on the chassis. Tomorrow i switch the tubes to check of course...

What measurement point did you use for the bias voltage? Swapping the position of the power tubes is a good idea. You can also verify that the bias voltage at pin 5 of teach poser tube is the same. You can even do that in standby mode or without the power tubes installed at all.

[tepsamps]

The bias voltage is almost the same at pin 5, -35 V. But i took the voltages of the OT, i can't believe what i see

Before swapping the tubes : CT : 448 V Blue : -13 V Brown 442 V
After swapping the tubes : CT : 448 V Blue : -10 V Brown 442 V

The OT is dead ? Why is it working ? The "blue" tube is giving more light than the others ...

Without the tubes : CT 498 V Blue 495 V Brown -3 V ????

And the resistance is 200 R one side, 10 M the other side ???

I can't anderstand how it gives sound and power...

[Helmholtz]

One side of the OT primary (blue wire) is open, so only one power tube is working and amplifying a halfwave only.
Explains all your symptoms.
The non working tube draws a huge screen current of 17mA, likely causing tube damage.

[tepsamps]

One side of the OT primary (blue wire) is open, so only one power tube is working and amplifying a halfwave only.
Explains all your symptoms.
The non working tube draws a huge screen current of 17mA, likely causing tube damage.

OK, that's what i was scared of...
The replacement is about 60 €... And can be changed fast...

[Tom Phillips]

The bias voltage is almost the same at pin 5, -35 V. But i took the voltages of the OT, i can't believe what i see
Before swapping the tubes : CT : 448 V Blue : -13 V Brown 442 V
After swapping the tubes : CT : 448 V Blue : -10 V Brown 442 V...

Good work. I'm sorry we neglected to suggest, earlier in the thread, that you take those voltage readings.
It's a good lessen for all of us to keep in mind and it's a rare occurrence to find an open primary winding on an OT.
There is still the possibility that the fault could be where the Blue lead wire is connected to the winding. If so, since that connection is near the outside of the winding stack, you may be able to fix it.

[tepsamps]

Hello all,
I have changed the OT, and i still have weird results, not the same ones, but strange.

I tried 2 pair of 6V6, the one i used for the repair, EH, and new ones i just bought, shuagang...

B+ 430 V after the choke 426,5 V bias after the pot -42.5 V

Left Tube Right Tube

Plate 420 422
Grid -36 -40
G2 428 430
K 36.7 mV 26.3 mV


With both pairs of tubes, i have a big unbalance left/right and why G2 voltage is higher than the plate?

And the amp is not silent, but no farting noises

What happens...?

I think i should change the 220 K bias resistors first...